Carefully take the panel out. Note that the cut-out line is somewhat so-so, which is unimportant as long as the cut remains INSIDE of the panel lines. Any irregularities can be filed away later.  

Please note that this technique applies only if the inside panel is "lost", since the saw takes away about 0.3mm of material. 

On the photo, you can see both "flipper" doors, left finished, right freshly cut out.

Build the interior walls of the door well. Evergreen styrene strips are best suited for this. You can get them in any good modeling shop, in various sizes and shapes. I measure the length to be cut with a divider, and report the length to the Chopper. 

The Chopper is a handy tool allowing you to do neat cuts in styrene, and any angle, or cut series of same length bits in very little time.

The door walls, viewed from the backside. Walls are simple pieces of styrene glued together. Note the left well, already painted. In fact the color should be white, I will address this at a later stage. 

Things start to get serious. Take a piece of brass sheet (0.15mm thick) which will become the "flipper" door. Measure the dimensions (with the divider again). In this case, 20 x 12 mm would be perfect, allowing a little bit "extra" for try and error. 

Brass sheets can be bought at www.micromark.com, in various sizes and thickness (I have no interest in the shop!). The best way to trim them is regular scissors.  

One more hint for today: cut marks are best scribed on brass, since pencil graphite mines 

The flat piece of brass needs its fore end to be curved, and the aft end to remain flat. I used a wooden jig and rods of various diameters. Both came with the "Hold and Fold" tool I bought a couple of months ago at www.thesmallshop.com (again, I have no interest in the company).

Apply the brass piece against the step of the tool, and gently rub the wooden rod over it, to start curving the brass. Remember: one end has to remain flat, that is why I position the brass at an angle. Start the curving job with the thicker 8mm rod. Rub alternatively the left, and the right side of the flipper.

As the brass takes it shape, switch to a smaller diameter rod, 6mm in this case. This will help to "over-curve" the brass, since it has some elasticity, and will spring back to a wider curve as soon as you release the pressure. Note how nice the shape becomes.

The marked area is cut away, with regular scissors. 0.15mm brass is very easy to cut with scissors, although it tends to bend slightly at the end of the cut. You can easily fix this with pliers, or a small hammer and a jeweler anvil. Note that hammering brass leaves nasty bumps, so it is not the best method.

Note the nicely bent fore end? All done with the wood rod and bending tool (see steps 6-7)

It is time now to trim the edges we folded in the previous lesson. Scissors are the best tool to do this. Note that scissors tend to curl the brass slightly. but you can easily fix this with pliers.

Next is the flat aft end of the flipper. Again the "Hold and Fold" tool helps a lot, although you can achieve the same effect with regular pliers.

The nearly finished flipper now requires some fine-tuning to fit into the housing. I used a coarse grit Flex-I-File (www.micromark.com), but again, any other filing / sanding system works. Note the nice 3D shape of the flipper? Remember: you started with a FLAT piece of brass!

This is the only step that requires a special tool: You need to open the fin slip in the flipper. A milling machine is very convenient for this job. The greatest difficulty is to align the flipper correctly, to have a perfectly centered slot. 

Alternatively, you can drill two small holes at each end, and cut the slot open with a jigsaw. Sanding / filing will be required then, to obtain a neat slot.